When Kimberly Hester of Cass County, Mich. posted with permission a photo a coworker sent her on Facebook, she didn't think it would offend the public school where she taught, or lead the superintendent to demand access to her Facebook page. But a photo of her coworker with her pants down did just that.

Hester, 27, was a full-time peer professional, or teacher's aide, at Frank Squires Elementary in Cassapolis, Mich. for about two years. A year ago, in April 2011, a coworker texted a photo showing herself with her pants around her ankles, with the message "thinking of you" as a joke.

"She's actually quite funny. It was spur of the moment," adding that there was nothing pornographic about the picture, which only showed the pants, part of her legs, and the tips of her shoes.

"I couldn't stop laughing so I asked for her permission to post it [on Facebook]," she said. The coworker agreed. Hester said all this took place on their own time, not at or during work.

Hester said a parent (not of one of her students) showed the photo to the superintendent, calling it unprofessional and offensive. Hester said the photo could only be viewed by her Facebook friends. The parent happened to be a family friend.

In a few days, the superintendent of Lewis Cass Intermediate School District, Robert Colby, asked Hester to come to his office.

"Instead of asking to take the photo down and viewing it from my friend's point of view, they called me into the office without my union," she said. Hester is a member of the Michigan Education Association, which represents more than 157,000 teachers, faculty and support staff in the state, according to its website.

The superintendent asked that she show her Facebook profile page.

The Facebook photo in question (Courtesy Kimberly Hester)

"I asked for my union several times, and they refused. They wanted me to do it right then and there," Hester said.

Colby did not immediately return a request for comment.

A letter from the Lewis Cass Intermediate School District said, "…in the absence of you voluntarily granting Lewis Cass ISD administration access to you[r] Facebook page, we will assume the worst and act accordingly."

Robert McCormick, a professor at the Michigan State University College of Law, said normally in the private sector and in a non-union setting there is nothing to prevent an employer from asking for access to a Facebook page. But in a private sector setting, if an employee is summoned to a disciplinary meeting with the employer and requests union representation at that meeting, it is an unfair labor practice to refuse that representation.

"I would be surprised if Michigan law did not follow the same standards," he said.

Louis Chism, the school district's special education director, wrote in an email to ABC News, "At this time it would be inappropriate for me to comment on any aspect of this situation."